Here is one of the most brutal and most demanding drills for special operations forces. The special purpose unit of US Marine Corps, 24th Marine Expeditionary Unit, which is trained to work in all environments, including water is subdued to the complicated and abnormal stress test.
They actually are learning how to escape from a submerged helicopter while conducting training at the HUET (Helicopter Underwater Egress Trainer) aboard Camp Lejeune. The drill itself checks their level of fitness and mental readiness to act under brutal conditions while practicing how to safely leave the helicopter that landed in the water. The Marines are seated tight and blindfolded.